According to the fairly developed technology for producing conventional grain-oriented (CGO) silicon steel, MnS is adopted as the major inhibitor, and the heating temperature is higher than 1350° C. during hot rolling. Thus, the energy consumption is relatively high, and slag is introduced on the surface of steel billet under such a high temperature. The heating equipment needs regular cleaning, which impacts the output of the product, adds to the energy consumption, raises damage probability of the device, and promotes production cost. Therefore, a great deal of study has been carried out by both native and foreign researchers to lower the heating temperature of silicon steel. According to the developmental trend, there are two ways to modify the technology in terms of the heating temperature range. One way is to control the heating temperature in the range of 1150-1250° C. during hot rolling, which is referred to as low-temperature slab heating technology, by forming inhibitor in later stage via nitriding to acquire inhibition capability. At present, the low-temperature slab heating technology witnesses rapid development, as shown by, for example, U.S. Pat. No. 5,049,205, Chinese Patent CN 1978707 and South Korean Patent KR2002074312. However, additional nitriding equipment is needed in these methods, leading to increased cost and inconsistent magnetism of the final product due to uneven nitriding.
In the other way, the heating temperature is held in the range of 1250-1320° C. during hot rolling. As distinguished from the low-temperature technology, this may likely be referred to as medium-temperature slab heating technology. According to the medium-temperature slab heating technology, an inhibitor containing Cu is used, and the smelted and continuously cast slab is subjected to twice cold rollings, between which intermediate decarburizing annealing (one-off decarburizing annealing) is carried out to lower the carbon content to less than 30 ppm. After the secondary cold rolling, the MgO separator is coated immediately or after recovery annealing at low temperature, followed by high-temperature annealing and subsequent treatment. The technical solutions disclosed in European Patent EP 0709470 and Chinese Patent CN 1786248A belong to the medium-temperature slab heating technology. The common problem of these two patents is the excessively low content of sulfur, which leads to inadequate amount and uneven distribution of the inhibitor. As a result, local or entire inhibiting capability is impacted, so that secondary recrystallization is not brought about to its full extent, and magnetic performance is degraded and unhomogenized.